Good afternoon. Faced such a problem:

Steps to reproduce:

1.      Create a panel
2.      I click to change the panel
3.      Adding a page
4.      I add 26 graphs to the page.
5.      I keep
6.      The following pages, which were created in advance, disappear

The screenshot shows that there are 5 pages and there were 7 of them - 2 pieces disappeared somewhere after saving.